1. Technical Field
The present application relates to semiconductor technology, and more particularly to methods of depositing polysilicon and forming polysilicon structures.
2. Related Art
Polysilicon is a regularly used material in semiconductor processing in the fabrication of semiconductor devices. Examples of polysilicon structures include gate structures of a semiconductor transistors and semiconductor memory cells. Formation of these polysilicon structures should ideally result in a predictable structure in order to achieve desired device characteristics. However, as the scale of semiconductor devices continues to shrink, the formation of desirable polysilicon structures becomes increasingly challenging.
One specific example of a polysilicon structure is the floating gate of a flash memory device. Some floating gates are formed using self-alignment processes, whereby the gate structures are automatically aligned with neighboring isolation structures. An example of a process for manufacturing a self-aligned floating gate formed of polysilicon material is disclosed in U.S. Pat. No. 7,459,364 to Lee et al. (“Lee”), which is hereby incorporated herein by reference.
Lee discloses a process for achieving an intermediate semiconductor structure similar to the structure shown in FIG. 1. FIG. 1 shows a cross-sectional view of a semiconductor substrate 100 in which a series of field isolation structures 102 have been formed. The field isolation structures 102 are provided to isolate neighboring active regions. The field isolation structures 102 define a series of trenches 104, where gate structures will be formed. Turning next to FIG. 2, subsequent processing steps result in formation of a tunnel dielectric layer 106 and a conductive structure 108. The conductive structure 108 can include polysilicon that is formed by a deposition process, such as a Chemical Vapor Deposition (CVD) process. The manufacturing process could continue with material removal and planarization processes, such as CMP, for removing upper portions of the conductive structure 108, such that floating gates are formed between the field isolation structures 102 in the trenches 104.
However, as shown in FIG. 2, a defect in the form of a void 110 can sometimes occur during deposition of the polysilicon of the conductive structure 108. Such voids can occur because the polysilicon grows inward from the sidewalls of the field isolation structures 102 during the deposition process. As semiconductor devices continue to shrink, the aspect ratio (ratio of depth to width) of active-area trenches defined by neighboring isolation structures 102 tends to increase, which increases the likelihood that defects such as voids 110 can occur.
It would therefore be desirable to provide an improved polysilicon deposition process that decreases the likelihood that defects such as voids occur during a semiconductor manufacturing process.